This invention relates to propylene polymerization catalysts and particularly relates to catalyst systems which produce commercially acceptable levels of low molecular weight and, especially, substantially amorphous polymers as determined by the amount of polymerized product which is soluble in n-hexane at room temperature ("Hexane Solubles").
The polymerization of propylene to normally-solid, substantially crystalline polymers using heterogeneous catalysts comprising transition metal halides and aluminum alkyls now is well known in the art. However, there is a continuing need in the industry for complete catalyst systems which produce a high yield, as measured by the grams of crystalline product per gram of transition metal halide consumed, while producing a minimum amount of Hexane Solubles. In a slurry polymerization process which uses a hydrocarbon solvent, such as n-hexane, amorphous and low molecular weight polymer accumulates in the solvent which necessitates extensive solvent purification procedures. Since the economic value of such n-hexane-soluble polymer is lower than normally-solid, substantially crystalline product, the overall process becomes less efficient as the amount of Hexane Solubles increase. A commercially desirable catalyst system would produce low amounts of Hexane Solubles while maintaining reasonable yields. The product produced using such catalyst system desirably has acceptable odor and environmental qualities. Also desirable is a low concentration of residual titanium.
In a solventless, liquid-phase bulk polymerization or in a gas phase process, the production of polymers which contain more than about 2% of Hexane Solubles requires a separate extraction procedure to produce commercially acceptable products and makes these inherently efficient processes uneconomical. Therefore, polymerization processes which produce low amounts of Hexane Solubles while not adversely affecting polymerization yield are in demand.
Various catalyst modifiers in addition to transition metal halides and aluminum alkyls have been disclosed to minimize Hexane Solubles in alpha-olefin polymerization. Such modifiers include aromatic or aliphatic amines, esters, amides, phosphites, phosphines, phosphine oxides, aldehydes, tetraorganosilyl compounds such as tetraalkyl-, tetraaryl- and tetraalkoxysilanes, sterically hindered cyclic amines, amine N-oxides and organotin sulfides. Known catalyst modifiers include the combination of the hydrogen sulfide, sulfur dioxide or bis-(tributyl)tin sulfide with an aromatic amine or amine oxide such as lutidine, collidine (2,4,6-trimethylpyridine) and lutidine-N-oxide. Specific catalyst systems including such combinations of modifiers are described in U.S. Pat. Nos. 3,950,268 and 4,072,809 both incorporated by reference herein. Although such modifiers do tend to decrease Hexane Solubles, they or their reaction products may produce undesirable odor or other effects in polymeric product.
Molecular weights of alpha-olefin polymers have been controlled by addition of "hydrogen active" compounds such as mineral acids to the olefin stream or directly to the polymerization reaction (U.S. Pat. No. 3,161,628). U.S. Pat. No. 2,971,950 discloses adding anhydrous hydrogen halide or alkyl halide to an alpha-olefin polymerization to control molecular weight. U.S. Pat. No. 3,271,381 uses 0.5 to 3 gram-equivalents of a strong acid per gram-atom of titanium to control molecular weight of polyolefins.
The use of halogen acids, e.g., HCl or HBr, to treat catalyst supports is taught in U.S. Pat. Nos. 3,658,722 and 3,888,789. Hydrogen chloride gas has been incorporated in alpha-olefin polymerization to produce elastomers (U.S. Pat. No. 3,563,964) and to change polymerization to a cationic process (U.S. Pat. No. 3,692,712). U.S. Pat. No. 3,275,569 teaches reducing titanium tetrahalide with aluminum in the presence of a hydrogen halide to form a polymerization catalyst component, while U.S. Pat. No. 2,256,264 teaches a polymerization catalyst system from a halogenated metal of groups IVa, Va, or VIa (e.g. TiCl.sub.4), aluminum chloride, hydrogen chloride and powdered aluminum. U.S. Pat. No. 3,121,064 teaches regenerating a titanium halide catalyst component with dry halogen chloride. Sulfur dioxide and sulfur trioxide have been disclosed to treat an olefin polymerization catalyst component consisting of a titanium or vanadium compound supported on a metal oxide or hydroxide (U.S. Pat. No. 4,027,088 and British Pat. No. 1,492,549).
Certain mineral and organic acids and anhydrides have been used in olefin polymerization systems which do not employ an organoaluminum-transition metal compound catalyst to form crystalline polymers. References to such systems are made in U.S. Pat. Nos. 3,426,007, 3,476,731, 3,497,488, Re. 29,504, 3,676,523, 3,686,351, 3,850,897, 3,896,087, and 4,029,866.
Carboxylic acids have been added to ethylene polymerization to reduce deposition of polymer on reactor walls (U.S. Pat. No. 3,082,198). Alkali metal salts of inorganic oxyacids have been used in an olefin polymerization catalyst comprising an aluminum sesquihalide and a transition metal halide (U.S. Pat. No. 3,400,084). Acid and base ion exchange resins have been used in olefin polymerization systems to produce crystalline polymer (U.S. Pat. No. 3,595,849).
An object of this invention is to produce catalyst modifiers which decrease Hexane Solubles while maintaining reasonable polymerization activity. A further object of this invention is to produce a polymeric product having acceptable odor. Other objects are described herein.